The crash was reported around 11 a.m. in the Webster Tube from Oakland to Alameda and involved at least two vehicles, CHP Officer Peter Van Eckhardt said.
All the lanes of both tubes were blocked for about 20 minutes and one lane on the Alameda side has since reopened, according to Van Eckhardt.
Van Eckhardt did not know if anyone was injured.
Traffic in the area is extremely heavy and backed up to Interstate Highway 880 on the Oakland side of the tunnel, according to Van Eckhardt.
A Sig-alert was issued at 11:26 a.m. There is no estimated time when the remaining lanes will reopen.